This invention relates to blood sampling containers such as tubes or bottles and to stoppers or closures therefor.
Containers are for the present provided in hospitals, clinics an the like for use in blood sampling in various forms to suit differing particular requirements as dictated by medical and/or financial factors. At their simplest blood sampling tubes or bottles are provided either with a screw thread to be closed with a screw cap or with a plain neck closed by a deformable press-on cap or a cork or similar plug. The former arrangement can be made to various tolerances and hence seal but in general the finer the tolerance, the greater the cost; the latter has the benefit of cheapness of manufacture both of tube or bottle and of the closure means but the seal afforded is generally not up to the highest medical requirements. For such uses it is frequently the case that the stopper or closure must be capable of holding a vacuum in the tube or bottle and to achieve this reliance is usually placed upon the use of tight fitting rubber or butyl rubber stoppers or bungs in tubes or bottles having plain ends or necks. The tight fit is achieved by providing a portion of the stopper or bung with an external diameter slightly greater than the internal diameter of the tube which it is to fit, the compression of the rubber against the glass or similar material of the tube or bottle providing a vacuum seal.
It is with such vacuum holding blood sampling containers with which the present invention is particularly concerned but it is anticipated that the container and closure arrangement of the invention could well find widespread use in circumstances where economics previously dictated the use of an arrangement with a lower specific performance.
The rubber stopper or bung arrangement discussed above presents substantial disadvantages. Firstly removal of the closure can be difficult for laboratory personnel bearing in mind that this usually needs to be effected single handed and even when the closure is provided with an upper portion of diameter marginally greater than that of the tube end or neck, this difficulty may lead to traumatised thumbs and/or a reduction in the speed of processing. Furthermore removal of a rubber bung from a closed container is believed to create what is known as the "aerosol effect"--a sudden change in pressure resulting in vaporisation of part of the contents of the container. This can be dangerous, particularly if the blood in the container is contaminated for example with hepatitis virus. The aerosol effect is generally the greater as the size of container increases. A part of the rubber of the closure will be in contact with the blood within the container; on removal of the closure contamination of laboratory personnel and of surrounding surfaces may be difficult to avoid even should the "aerosol effect" not occur. As a final example of user related problems, the replacement of a rubber closure on a partially filled container may be followed by expulsion of the closure due to the increase pressure produced within the container. The greater the mass of the closure, or at least the greater the length of closure which enters the container neck, the more likelihood of expulsion.
To turn to manufacturing and supply difficulties, the cycle time of rubber moulding is high as against generally used plastics materials, the cost, weight for weight, likewise being substantially higher for rubber materials as opposed to generally used plastics materials. Furthermore the need for a close internal fit for various container sizes necessitates provision of a number of sizes of closure with consequent increase in tooling costs and the levels of stocks required, this being made the worse as hospitals, clinics and the like require provision of closures in a number of different colours to assist in cataloging and the like. This can increase the requirement for stock levels perhaps a further 6 to 10 fold. In manufacturing too the colour coding can cause further difficulties relative to plastics materials as rubber materials are by and large considerably less receptive to subtleties of colouration and more expensive as a result.